I have seen the picture before, but it wasn’t until now that I figured out the Helmholtz double entendre.
Helmholtz resonation is a way to enhance certain frequencies by blowing air into a cavity shaped to resonate with the desirable frequencies, named after German scientist Hermann von Helmholtz.
Helm means helmet in German. Holtz means wood in German (nice name: wooden helmet?) but in most other languages it resembles the word “hold” making this a helmet held Helmholtz resonator. Say it fast.
Correctly it would be ‘Holz’ and not ‘Holtz’
The latter I’ve heard as a family name sometimes. But you’re probably right, that it historically referenced ‘Holz’
Edit: only found a German page about the origins of the name, and yes, it is very probably coming from forest, woodland, wood
